Tuesday, December 14, 2004

I'm not sure if I'm the only person who's not using JOGL to do animation, but I seem to have a problem where when I resize a JOGL window, it fails to update its screen correctly. Most people don't encounter this because if they constantly update their screen inside an animation loop, any update failures will correct themselves during the next pass through the animation loop. A quick search through Google brings up nothing.

What happens is that if I use the November 19th build of JOGL, when I resize the window, I get a blank white screen. When I resize it again, I get my image displayed correctly again.

I suspect that the problem has something to do with double-buffering after a resize. Here is my evidence:

a) when I do successive resizing, it alternates between being ok and not being ok
b) after I do a resize, cover the window, and uncover the window, the window looks fine again
c) if I create a single-buffered OpenGL context, JOGL keeps dumping stack traces to the console
d) The following bit of code looks suspicious:
if (autoSwapBuffers && !isReshape) {swapBuffers();}

Still, when I trace through the execution of the code, everything seems to trigger correctly, so I suspect that maybe I'm just doing something incorrectly in OpenGL or elsewhere. If I force an extra buffer swap after a reshape, everything does seem to work correctly (the white screen still shows, but it's quickly overwritten during the successive call to display). Perhaps it's a driver problem. I should try this on a different machine.

Sunday, December 12, 2004

This isn't a real post but more of a rant session about the quality of the X3D specification. This spec is of mediocre quality at best. It's quite clear that they revised the spec many times and forgot to clean up references to old revisions. For other parts of the spec, they seemed to be describing an existing implementation as opposed to specifying how new implementations should behave (i.e. they leave out important details). Various parts of the spec are inconsistent or confusing. Worst of all, some parts of the spec give off the impression that they've NEVER BEEN IMPLEMENTED.

I've only tried to implement a very small amount of the specification so far, but here are various problems I've seen so far:

1. A lot of the example interfaces for the Java language bindings are inconsistent with other parts of the specification or are simply wrong.

2. The Java language bindings have clearly never been implemented or tested.

3. Default values are defined for several field instances when they are simply the same as the defaults for fields themselves

4. They never really make it clear what their notation for node fields are

5. Various inherited fields are listed repeatedly over and over again

I suppose it's a little worse for me because I'm autogenerating code based on the specification, so things that would be glossed over by someone implementing the specification by hand really cause problems for me. Oh well. So far, I haven't hit any part of the spec that was so outrageously wrong that I couldn't figure out what they had intended, so maybe things aren't so bad after all.

Friday, December 10, 2004

After spending more time trying to understand the X3D spec, I think I've decided that it is simultaneously less ambitious and more ambitious than I had expected. I had initially thought that X3D intended to define specifications for a lot of the annoying 3D programming issues like file exchange, scene graphs, etc. This way, programmers could just use some X3D components instead of having to code their own lower layer 3d code. Based on what I had read from the spec and about the history of X3D, I thought that that's what X3D was for. I'm a little skeptical of that idea, but it does sound intriguing. I'm actually a little disappointed that this isn't wasn't X3D was aiming to do. In fact, X3D seems to be just a standard for a 3d media player/browser. They've essentially designed a file format for X3D media and an API for talking with X3D browsers. If X3D were a database, the X3D specification would describe the file format of the database, an RPC framework for communicating with the database, and a general description of how the database should behave. This is an ambitious vision, but it isn't as generally useful as having a bunch of lower-level components. Hopefully when the 3D Industry Forum comes out with their competing spec, it'll be possible to compare which approach is more useful. I suppose that it's like the difference between white-box and black-box inheritance. Oh well.

In any case, generating code using XSLT seems to work pretty well. It's a little verbose, and you have to watch for those <> characters in the code, but I've been pretty satisfied so far. Hopefully, if all goes according to plan, I'll have a rudimentary partial implementation of a few nodes from the SAI layer of X3D by Monday. Then I can actually start cobbling together a renderer and parser.

Thursday, December 09, 2004

So, I somehow committed myself to making a simple X3D browser for mobile devices, but it's really hard to figure out where to start. I've been browsing the specification for several days now, and it's just not really sinking in. Usually, the reference implementation (xj3d) would be the normal place to start, but it's really a VRML browser with a thin veneer of X3D on top of it. In any case, most of xj3d seems to be hand-coded, but the specification looks really amenable to automatic generation, which is the route I want to take.

In order to code up a browser, you need a simple 3d engine first. Since X3D defines a scene graph API, it seems like that working on that API would be an ideal place to start (since one can use a scene graph as the base for a 3d engine), but the more I read about the X3D scene graph API, the more I realize that it's inappropriate for doing any sort of rendering from it. Plus, the interface for getting a browser instance seems cumbersome to code up as well. Still, I suppose it's as good a place to start as any.

For the code generator, I was originally thinking of coding something up in Java, but I think I might make an attempt at putting something together in XSLT. I'm not sure if it'll work, but it's always good to use existing standards, so I suppose it's worth a try. Of course, XSLT doesn't support generating multiple output documents from a single input document, so I'll still have to write some sort of coordinator or something.

I guess I'll start with something simple by auto-generating the exception classes. Already, there are some pecularities in the spec, because initially they define a bunch of abstract language-independent exceptions and then later in the spec, they decide that for the Java version, they'll use a different set of exceptions using a completely different naming scheme. This is actually sort of annoying; I think it's a bug in their spec.